Dissertation / PhD Thesis/Book

PreJuSER-51105

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Grundlegende Untersuchungen zur Korrosion von Al$_{2}$O$_{3}$ durch Metallhalogenidschmelzen und zur Thermochemie korrespondierender Korrosionsphasen

Möllenhoff, M. (Corresponding author)FZJ*

2006
Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag Jülich

Please use a persistent id in citations: http://hdl.handle.net/2128/535

Report No.: Juel-4214

Abstract: Ceramic discharge vessels in metal halide lamps made of polycrystalline alumina (PCA) instead of quartz glass find application at higher temperatures and this results in increased efficiency of the lamps. Discharge vessels contain a mixture of various metal halides like NaI, DyI$_{3}$, CeI$_{3}$, which influence the spectral properties of the lamps. Under operating conditions, these metal halides form, apart from the gas phase, a liquid phase also. In particular the liquid phase reacts with the wall material PCA resulting in the formation of rare-earth-aluminates. Furthermore, a transport of aluminum oxide, along a temperature gradient parallel to the vessel wall, takes place. This transport results in reduction of wall thickness and finally causes a leakage in the vessel wall. The corrosion of the wall material is the most frequent reason for the failure of the lamps. The aim of the investigations presented in this work is to elucidate the particular influence of the liquid phase in the corrosion and the chemical transport of Al$_{2}O_{3}$. For this purpose, solubility data of Al$_{2}O_{3}$ in lamp-relevant salt systems were determined by isothermal annealing experiments. The observed corrosion phenomena were described and interpreted with respect to the temperature distribution inside the burner vessels and the compositions of the halides. Additionally annealing experiments in a temperature gradient were conducted. Furthermore thermodynamic data for the corrosion phases $Dy_{3}Al_{5}O_{12}$, DyAlO$_{3}$ and $Dy_{4}Al_{2}O_{9}$ were determined by the method of Knudsen Effusion Mass Spectrometry. The present work shall contribute to model the observed corrosion processes in order to increase the lifetime of the lamps by selective means.

Note: Record converted from VDB: 12.11.2012
Note: Aachen, Techn. Hochsch., Diss., 2005

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Contributing Institute(s):

1. Werkstoffstruktur und Eigenschaften (IWV-2)

Research Program(s):

1. Rationelle Energieumwandlung (P12)

Appears in the scientific report 2006

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Database coverage:

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